This invention relates generally to vehicle suspension systems, and, more particularly, relates to vehicle shock absorbers or dampers that provide variable damping in response to changes in vehicle movement.
The basic components of conventional dampers are a piston and piston rod operating inside a fluid filled cylinder, fitted with suitable piston seals and piston rod seals. Various orifices are provided either in the piston or in the cylinder to adjust the resistance of the damper to relative axial movement between the piston rod and the cylinder. The ends of the piston rod and cylinder are provided with fittings for attaching the damper between the sprung mass (body) of the vehicle and the unsprung mass (wheel and suspension components) of the vehicle.
Several configurations of dampers are currently in use, some of which use compressible gas under pressure, with or without an additional piston or external reservoir, to allow for the varying volume inside of the unit as the rod moves in and out of the cylinder. Other types use an un-pressurized reservoir to store the excess fluid when the rod enters the cylinder. Still other configurations, no longer in wide use, employ a lever that operates the damping element.
Damping characteristics of conventional shock absorbers are a compromise between the requirements of acceptable ride comfort and the reqirements for good handling. In order to provide a smooth ride, the force passed to the body from the wheel by the damper when traversing a bump should be low. For handling, the shock absorber must firmly damp the rolling and pitching of the body with lateral and longitudinal accelerations. The ride/handling compromise occurs because hydraulic dampers are sensitive to piston/cylinder velocity, and the velocity of the piston relative to the cylinder is similar for certain bump conditions and roll/pitch conditions. Damping roll and pitch with sufficient firmness to provide good handling thus imposes a damping rate that is excessive for smooth ride.
Typical shock absorbers address this problem by partially linearizing force/velocity characteristics. This approach, which recognizes that orifices pass fluid in proportion to the square-root of the pressure across them, utilizes multiple metering orifices. A small bleed orifice is used to pass fluid at low velocities, and other orifices are opened by pressure regulating mechanisms (blow-off or pop-off valves) to reduce the damping force at higher velocities. Other valve and orifice configurations are also used to vary the characteristics as a function of velocity.
Some dampers are also sensitive to the axial position of the piston, such that the damping action is soft near the center (small ride motions) and stiffer near the ends. Shock absorbers of this type are referred to as "stroke-sensitive."
In recent years many electronic or electrically variable shock absorbers have been introduced. These devices allow the shock absorber force/velocity characteristics to be varied as a function of driver choice or other sensed variables, including steering wheel angle, brake application (typically on motorcycles), laterally or longitudinally mounted accelerometers, or other sensing devices. These dampers often utilize a microprocessor or other computing device. The variability offered by these dampers reduces the ride/handling compromise. Such dampers are referred to as adaptive suspension components.
Examples of variable damping systems are disclosed in the following patents:
U.S. Pat. No. 4,478,431
U.S. Pat. No. 4,586,728
U.S. Pat. No. 4,589,676
U.S. Pat. No. 4,591,186
U.S. Pat. No. 4,647,069
U.S. Pat. No. 4,671,534
U.S. Pat. No. 4,720,084
EPO 224,815
EPO 238,977.
U.S. Pat. No. 4,478,431 discloses a vehicle suspension having load-dependent damping. The hydraulic dampers include a pressure-responsive spring-loaded valve controlling a metering orifice. Damping rate increases with increasing hydraulic pressure, which depends on the laden weight of the vehicle.
U.S. Pat. No. 4,586,728 discloses an adjustable suspension system in which sensors detect vehicle speed and engine power output. Above a pre-set acceleration rate, a control circuit transmits signals to increase the damping rate of the shock absorbers.
U.S. Pat. No. 4,589,676 discloses an adaptive ride-control system in which adjustable hydraulic dampers are regulated by a control circuit in response to the amplitude of vertical oscillation of the wheels.
U.S. Pat. No. 4,591,186 discloses an adjustable damper in which an external automatic controller, responsive to brake fluid pressure, vehicle speed and steering wheel angle, selects between high and low shock absorber damping rates.
U.S. Pat. No. 4,647,069 discloses an adjustable suspension system having coordinated ride-height control and adjustable damping. A ride-height sensor transmits electrical signals to a controller that directs an electrical actuator to provide an inverse relationship between damping force and ride height.
U.S. Pat. No. 4,671,534 discloses a suspension system that increases damping rates in response to vehicle speed and sensed lateral forces. A control unit calculates lateral acceleration based on signals from a speed sensor and pressure sensors on the left and right sides of the vehicle.
U.S. Pat. No. 4,720,084 discloses a hydraulically damped engine mount. The mount includes two chambers separated by a control valve. Operation of the control valve is controlled in part by an inertial damping mass coupled to the control valve by a variable hydraulic clamp circuit. The control pressure of the clamp circuit can be varied to provide various damping characteristics.
EPO Patent No. 224,815 discloses an adjustable hydraulic damper having flow-controlling ducts that are opened or closed by solenoid elements.
EPO Patent No. 238,977 discloses a suspension system having a variable shock absorber. The effective stroke and damping rate of the shock absorber are varied by an external adjuster, whose setting is regulated by an external controller in response to vehicle and road conditions.
Conventional electronic or electrically variable shock absorbers, however, are expensive, difficult to manufacture, and often require re-design of other existing suspension or body components to provide support and clearance. Typical electronically-variable dampers also require external sources of power (electrical, mechanical, hydraulic, or other) and the use of microprocessors, which increase complexity and reduce reliability.
It is accordingly an object of the invention to provide improved variable damping apparatus.
Another object of the invention is to provide damping apparatus that dynamically varies damping rates in response to lateral or longitudinal--i.e., horizontal--acceleration of the vehicle.
It is a further object of the invention to provide adaptive damping apparatus that is self-contained and operates without external sources of electrical power.
Another object of the invention is to provide adaptive dampers that are reliable, easily manufactured, and readily adaptable to existing suspension systems.
Other general and specific objects of the invention will in part be obvious and will in part appear hereinafter.